1. Field of the Invention
This invention relates to a lens barrel, and more particularly to a lens barrel suitable for use with a flashlight-emitting device to effect very proximate flash photography.
2. Description of the Prior Art
When auxiliary light photography has been effected with an object illuminated by an electronic flashlight-emitting device, the aperture value has been made variable to make the total quantity of light emitted by the flashlight-emitting device and the product of the object distance and the aperture value equal to each other. However, in very proximate photography, the object distance is very short and therefore, to obtain proper exposure, it has often been the case that a diaphragm opening smaller than the minimum diaphragm opening that can be adjusted by the diaphragm device of a camera is required. Thus, U.S. Pat. No. 4,034,387 or U.S. Pat. No. 4,068,245 discloses a technique in which the quantity of emitted flashlight is made variable with the object distance and the photographing magnification taken into account, whereby the object lying at a very proximate position is properly illuminated.
However, the conventional technique of this type has the following disadvantage although it has certainly increased the possibility of obtaining proper exposure during very proximate photography. That is, since there is a limit in the minimum value of the quantity of emitted light electrically adjusted, the conventional flashlight-emitting device becomes useless for an object for which proper exposure can be obtained only at a quantity of emitted light smaller than this minimum value.